1. Field of the Invention
The invention relates to an all terrain vehicle which is adapted for use on many different types of terrain but particularly for use in transition zones between water and ice, on soft surfaces, such as mud and snow, and negotiating steep walls of limited height.
2. Prior Art
There are many different types of all terrain vehicles, and these types can be classified on the basis of particular types of driven members or surface engaging means, which are dependent on the type of terrain the vehicle is most likely to encounter in normal use. For vehicles that are to be used mostly on hard, steep terrain, endless crawler tracks have been found satisfactory, but vehicles of this type generally have poor water performance if the crawler tracks are to be used as the sole means of propelling the vehicle on water. Commonly, an amphibious crawler track vehicle has an auxiliary water propulsion means, such as a propeller, which is lowered and engaged for use when the vehicle is on water, and raised and disengaged for use when the vehicle is on land. Also, vehicles using crawler tracks for use on hard surfaces commonly suffer from poor soft surface performance, such as encountered when traversing mud or soft snow, usually due to the weight of the vehicle and bearing area of crawler tracks. Commonly, crawler track vehicles have better hill climbing ability than wheeled vehicles due to increased bearing area of the driven member contacting the ground. However, with both tracked vehicles and wheeled vehicles a maximum angle of ascent is reached when the vehicle tends to tip over backwards due to height of the centre of gravity of the vehicle, and torque application to the driven member.
Apart from wheeled and tracked vehicles, many attempts have been made to use air cushion vehicles in marginal terrain, but commonly air cushion vehicles are limited to a shallow angle of ascent or descent, as well as overall surface undulations which must be limited to provide an adequate seal for the skirt that provides the air cushion.
One reason for tracked vehicles having poor water performance is that the upper run of the track, which moves in an opposite direction to the lower run, is commonly immersed in water and this tends to oppose the forward motion generated by the lower run of the track. This resistance to motion can be overcome by locating the upper run of the track above the mean water surface as shown in U.S. Pat. Nos. 2,487,397 issued to Swennes and 2,894,476 issued to Lindgren. The vehicles of these references are limited in their ability to climb from water onto land because, when climbing out of the water, the rear portion of the vehicle tends to sink, thus increasing angle of the vehicle as it attempts to climb on to the land. U.S. Pat. No. 3,842,785, issued to Rivet, discloses an amphibious marsh craft with crawler track supports which provide floatation to reduce sinking of the vehicle in water, but there appears to be no attempt to maintain the upper runs of the crawler tracks clear of the water.
U.S. Pat. Nos. 1,298,366 issued to Macfie, and 3,417,832 issued to Ziccardi, disclose complex mechanisms using articulated multiple crawler track arrangements which are adapted to negotiate severe changes of terrain gradients, such as short vertical walls. However, these vehicles appear to be only for use on land, and furthermore are highly complex and would likely present difficulties when used on soft surfaces or on water.
There are many devices utilizing two body portions supported on wheels etc., the body portions being connected together for swivelling or hinging movement about one or more axes of rotation. Typical devices are found in U.S. Pat. No. 3,057,319, issued to Wagner, U.S. Pat. No. 3,446,175, issued to Boehler et al, and U.S. Pat. No. Re. 27,642 issued to Enos. The body portions of these vehicles can move relative to each other, but it is felt that the wheels or other surface engaging means are inappropriate in very soft surface conditions, such as soft snow, and generally the vehicles likely would have poor climbing ability due to the relatively high centre of gravity of this type of vehicle. Two of the patents show independent propulsion means for propelling the vehicles in water, but these propulsion means require engagement of different driven means and thus would be difficult to utilize in a rapidly changing terrain in which water and ice or other solid materials are mixed together.
Some prior art vehicles with relatively high centres of gravity are prone to rolling about their longitudinal axes when laterally traversing a slope. These vehicles can roll unto their sides or tops and are not capable of regaining an upright position without external means.